One aspect relates to a cartridge system for mixing and applying a bone cement, with which the starting components of the bone cement is mixable in a closed cartridge to form a cement bone dough. One aspect also relates to a method for applying a bone cement.
Polymethyl methacrylate (PMMA) bone cements can be traced back to the groundbreaking work of Sir Charnley (Charnley, J.: Anchorage of the femoral head prosthesis of the shaft of the femur. J. Bone Joint Surg. 42 (1960) 28-30.). PMMA bone cements consist of a liquid monomer component and a powder component. The monomer component generally contains the monomer methyl methacrylate and an activator (N,N-dimethyl-p-toluidine) dissolved therein. The powder component, also referred to as bone cement powder, includes one or more polymers, which are produced on the basis of methyl methacrylate and comonomers, such as styrene, methyl acrylate or similar monomers by polymerisation, preferably suspension polymerisation, and includes a radiopaque material and the initiator dibenzoyl peroxide. As the powder component is mixed with the monomer component, a plastically deformable dough (the actual bone cement) is created by swelling of the polymers of the powder component in the methyl methacrylate and is usually referred to as bone cement dough. As the powder component is mixed with the monomer component, the activator N,N-dimethyl-p-toluidine reacts with dibenzoyl peroxide and forms radicals. The radicals formed initiate the radical polymerisation of the methyl methacrylate. The viscosity of the bone cement dough increases with continued polymerisation of the methyl methacrylate until the dough solidifies.
The monomer used most frequently in polymethyl methacrylate bone cements is methyl methacrylate. Redox initiator systems usually consist of peroxides, accelerators and optionally suitable reducing agents. Radical formation occurs only when all constituents of the redox initiator systems interact. The constituents of the redox initiator system are therefore arranged in the separate starting components such that they cannot trigger radical polymerisation. The starting components are then storage-stable with suitable composition. Only when the two starting components are mixed to form a bone cement dough do the constituents of the redox initiator system, previously stored separately as monomer liquid and powder, react, wherein radicals are formed, which trigger the radical polymerisation of the at least one monomer. The radical polymerisation then leads, with consumption of the monomer, to the formation of polymers, wherein the cement dough cures.
PMMA bone cements can be mixed in suitable mixing beakers with the aid of spatulas by mixing the cement powder with the monomer liquid. In so doing, air bubbles can become trapped in the bone cement dough, which can have a negative effect on the mechanical properties of the cured bone cement.
In order to avoid inclusions of air in the bone cement dough, a large number of vacuum cement mixing systems have been described, wherein the following are mentioned by way of example: U.S. Pat. Nos. 6,033,105 A, 5,624,184 A, 4,671,263 A, 4,973,168 A, 5,100,241 A, WO 99/67015 A1, EP 1 020 167 A2, U.S. Pat. No. 5,586,821 A, EP 1 016 452 A2, DE 36 40 279 A1, WO 94/26403 A1, EP 1 005 901 A2, EP 1 886 647 A1, U.S. Pat. No. 5,344,232 A.
EP 2 730 296 A2 discloses a thixotropic bone cement for vertebroplasty, in which the thixotropic properties are produced with a number of additives.
A development in cement mixing technology is provided by cement mixing systems in which both the cement powder and the monomer liquid are already packaged in separate compartments of the mixing systems and are only mixed with one another in the cement mixing system immediately before the cement application. Closed full-prepacked mixing systems of this kind have been proposed by EP 0 692 229 A1, DE 10 2009 031 178 B3, U.S. Pat. Nos. 5,997,544 A, 6,709,149 B1, DE 698 12 726 T2, EP 0 796 653 A2 and U.S. Pat. No. 5,588,745 A.
Patent DE 10 2009 031 178 B3 discloses a storing and mixing device as full-prepacked mixing system, in which the starting components necessary to produce the bone cement dough are already stored in the storing and mixing device and can be combined and mixed in the storing and mixing device. The storing and mixing device has a two-part discharge piston for closing a cement cartridge. Here, a combination of a gas-permeable sterilisation piston and a gas-impermeable sealing piston is used. This principle of a closed vacuum mixing system is realised in the PALACOS® PRO closed cement mixing system, which is produced and sold by the company Heraeus Medical GmbH.
With use of all previously known full-prepacked mixing systems, the medical user must perform a number of process steps at the devices in a predetermined order in succession until the mixed bone cement dough is produced and can be applied. If the process steps are muddled, this can lead to the failure of the mixing systems and can therefore cause disruptions in the surgical procedure. Costly training of the medical users is therefore necessary in order to avoid user errors.
WO 00/35506 A1 proposes a device in which bone cement powder is stored in a cartridge, wherein the cement powder fills the entire volume of the cartridge and the gaps between the particles of the cement powder are of a volume corresponding to the volume of the monomer liquid necessary to produce bone cement dough with the cement powder stored in the cartridge. This device is constructed such that the monomer liquid is introduced from above into the cartridge under the action of a vacuum, wherein to this end a vacuum is applied at a vacuum connection on the lower side of the cartridge. The monomer liquid is thus drawn through the cement powder, wherein the air disposed in the gaps between the cement particles is displaced by the monomer liquid. Here, a mechanical mixing of the formed cement dough by means of an agitator is omitted.
One disadvantage of this system is that cement powders, which swell quickly with the monomer liquid, cannot be mixed with this device, because the quickly swelling cement powder particles form a gel-like barrier once the monomer liquid has penetrated into the cement powder by approximately 1 to 2 cm, and hinder the migration of the monomer liquid through the cement powder as a whole. Under the action of a vacuum, it also cannot be ruled out that the monomer liquid might be suctioned off via the vacuum connection once the cement powder has been fully penetrated by the monomer liquid. There would then be insufficient monomer liquid available for the curing by radical polymerisation, or the mixing ratio might be modified undesirably, as could also the consistency of the bone cement. Conventional cement powders additionally demonstrate the phenomenon that the cement particles are only poorly wetted by methyl methacrylate on account of the different surface energies. The methyl methacrylate thus penetrates the cement powder only relatively slowly. It is also problematic that the air enclosed between the cement powder particles is to be displaced from top to bottom by the monomer liquid, because the air, which is specifically lighter than the monomer liquid, on account of the force of gravity, attempts to migrate upwardly in the cement powder rather than to migrate downwardly in the direction of the vacuum connection.
For these and other reasons, a need exists for the present embodiments.
In the Figures, like reference signs are also used in different exemplary embodiments for like or similar component parts for reasons of clarity and so as to be able to compare the exemplary embodiments.